1. Technical Field of the Present Invention
The present invention generally relates to Chemical Mechanical Polishing (CMP) of wafers, and more specifically to a multiphase CMP processing of wafers.
2. Background of the Present Invention
In the fabrication of semiconductor devices, metal conductor lines are used to interconnect the many components in device circuits. The metal conductor lines serve to interconnect discrete devices, and thus form integrated circuits. The metal conductor lines are further insulated from the next interconnection level by thin layers of insulating material and holes formed through the insulating layers provide electrical access between successive conductive interconnection layers.
In such wiring (conductor lines) processes, it is desirable that the insulating layers have smooth surface topography, since it is difficult to lithographically image and pattern layers applied to rough surfaces. Rough surface topography also results in 1) poor step coverage by subsequent deposited layers, 2) discontinuity of layers across steps, and 3) void formation between topographic features. Poor step coverage by deposited layers and void formation between topographic features result in degraded process yield and a decrease in the reliability of integrated circuits.
In semiconductor circuit manufacturing, CMP is one process used to produce smooth surface topography on insulating layers which separate conductive interconnection pattern layers. CMP can also be used to remove different layers of material from the surface of a semiconductor substrate. For example, following via hole formation in an insulating material layer, a metallization layer is blanket deposited and then CMP is used to produce planar metal studs. This is sometimes referred to as a etch-back step (i.e. a step of etching away an unnecessary portion of a metallic film such as a W (tungsten) film or an Al (aluminum) film formed on an insulating film having a contact hole, thereby exposing the insulating film).
Unfortunately, the current methods used for the CMP process to remove undesired portions of a metallic film often result in severely scratching the insulating film and conductor lines. This severe scratching can produce metal shorts between the conductor lines; and as a result the wafer must be scrapped. For example, if the metallic film to be removed is Al, then the current CMP methods convert the Al into Al(OH)x or (Al(O)x (also referred to as xe2x80x9cblack aluminumxe2x80x9d). The black aluminum can become embedded in the polishing pad and result in the severe scratching of the insulating film and conductor lines.
It would, therefore, be a distinct advantage to have a method and apparatus that would remove the undesired portions of a metallic film without severely scratching the insulating film or conductor lines. The present invention provides such a method and apparatus.
The present invention is a method and apparatus for CMP processing that reduces scratching of the insulating film and conductor lines of a wafer. More specifically, the method and apparatus introduce a cleaning solution to the polishing pad and wafer during various intervals of the polishing procedure.